| Molecular switches are being considered as the basis for novel functional materials with applications envisioned in molecular electronics and drug delivery devices. A lot of the design principles for creating these switches have been investigated using metallo-supramolecular architectures where oxidation of metal ions has been utilized as the driving force. As an alternative, the reduction of redox-active ligands can provide the stimulus for switching, however, it has not been explored until now. This novel modality of switching is investigated in this thesis by making use of pseudorotaxanes' rod-in-ring format, which lends itself to the preparation of molecular machines in the future. The primary redox-active ligand selected for this study is based on a tetrazine core: 3,6-bis(5-methyl-2-pyridine)-1,2,4,5-tetrazine. This bidentate ligand provides rich coordination chemistries for creating various architectures and facile reduction for driving switching.;First, electrochemical reduction of the tetrazine ligand is employed in the creation of a reversible switch where a phenanthroline-based macrocycle migrates reversibly between pseudorotaxanes. In a second example, reduction led to switching between two discrete architectures, i.e., from a pseudorotaxane to a grid corner and back again. The operating modes of these two different switches were verified by variable scan-rate cyclic voltammetry and digital simulations. Both processes occur via associative interchange pathways when they set off in their forward directions. For switching in the reverse direction, the macrocycle migration proceeded in a dissociative manner whereas the grid corner's conversion back to a pseudorotaxane was too fast for our electrochemical measurements. This mechanistic study provides some of the first insights into the details of switching in metallo-supramolecular systems.;An important discovery was made while investigating the switching between the pseudorotaxane and the grid corner complex. In the latter, where two tetrazine ligands are linked by a Cu(I) ion, one-electron reduction turned on electronic communication between the two ligands. This property, known as mixed-valency, has been extensively investigated in complexes where the ligand acts as a bridge to connect two redox-active metal centers. The work presented herein, therefore, inverts the role of ligand and metal. Spectroscopic, electrochemical and density functional theory investigations of this new kind of mixed-valent compound shows strong evidence for a fully delocalized Class III state, which is found to be present in dichloromethane and from room temperature down to -160 °C. By contrast, the crystal structure of a binuclear rhenium(I) tricarbonylchloro complex of the ligand 3,6-bis(5-methyl-2-pyridine)-1,2,4,5-tetrazine verified that the lowest-unoccupied molecular orbital of a complex with just one tetrazine core is localized to that single tetrazine ring system.;These studies further open up the possibilities for ligands to play increasingly functional roles in the creation of supramolecular architectures with switchable characters and of coordination compounds with novel electron-transfer properties. |
